Design of Iron Oxide-Flavin Nanocomposite Bacterial Cellulose Hydrogels

Abstract

In this work, a hybrid material based on bacterial cellulose (BC) hydrogels and magnetic photocatalysts was developed. Cellulose is capable of coordinating to metal oxides such as magnetic iron oxide nanoparticles (IONPs). When IONPs are coupled to flavins, naturally occurring photoactive isoalloxazine compounds, a heterogenous photocatalytic system is created that can integrate into BC, thus forming nanohybrid photoactive hydrogels. The hybrid gels have shown potential in their applicability to wastewater remediation due to their photoactivity, mechanical strength, porosity, durability, and biocompatibility. Ƴ-Fe2O3 IONPs were first synthesized using a microemulsion technique and coupled to a novel dopamine-flavin (DAFL) linker in water thus forming the first generation (gen1) of flavin-coated iron oxide particles (IONP-DAFL). The system proved capable of degrading amaranth (AMT) – a red azobenzene dye used in the textile industry – when irradiated with blue light for 3 hours in the presence of either 2-(N-morpholino)ethanesulfonic acid (MES) or ethylenediaminetetraacetic acid EDTA (0.1M, pH 6) as electron donors. Furthermore, the photodegradation reaction was successful both in an O2 environment and in Ar thus proving that the catalyst can successfully oxidize or reduce AMT. The problem, however, was the poor recyclability of the material in that the catalyst could not be reused more than once. To address this challenge, flavin structures containing phosphate binding moieties, flavin mononucleotide (FMN) and riboflavin phosphonic acid (RPA), were coordinated onto the surface of IONPs in water thus forming gen1 IONP-FMN and IONP-RPA respectively. However, additional improvements were needed to enhance the photostability and flavin loading of the gen1 catalysts thus resulting in the design of second generation (gen2) IONP-DAFL, IONP-FMN, and IONP-RPA, which utilized the same DAFL, FMN, and RPA ligands loaded onto the IONPs. However, the gen2 functionalization process was conducted in either acetone or methanol as opposed to water used in the gen1 coordination technique. Gen2 IONP-DAFL proved to be most effective of the 3 due to the dopamine’s higher affinity to iron oxide when compared to phosphate linkers. The photodegradation of AMT using the gen2 systems was done in the presence of white light irradiation and triethylammonium acetate (TEOA) (0.1M, pH7.5) as an electron donor. It was conducted in air as opposed to either in an O2 or Ar atmosphere and the recyclability was demonstrated for 3 cycles. Following the successful demonstration of photocatalytic activity, gen2 catalysts were embedded into BC hydrogels resulting in hybrid systems containing catalytic nanoparticles (BC-IONP-flavins). The gel containing dopamine-coated IONPs (BC-IONP-DAFL) was shown to successfully degrade AMT over 6 cycles in air under white light irradiation with TEOA (0.1M, pH7.5). BC-IONP-DAFL was also used for the photodegradation of aniline yellow (AY) – another azobenzene dye, estradiol (E2), and progesterone (PGS) in order to show the applicability of the catalyst in the degradation of other substrates. In this work, novel photocatalytic metal oxide-flavin nanoparticles capable of both oxidation and reduction of AMT under blue light irradiation were synthesized. Furthermore, a recyclable photoactive environmentally-friendly hydrogel was designed that can degrade AMT and other substrates using white light in air. The facile protocol used to create this new hybrid material can be implemented for the creation of magnetic nanohybrid gels useful for other applications such as DNA-sequestering and neuronal prosthetics.